This application relates to the art of braking systems, and more particularly to an antilock brake system (ABS) modulator relay valve. The invention is particularly applicable to a tractor or tractor-trailer type vehicle equipped with an air braking system in which a vehicle operator generates a control signal to operate a brake control valve. The signal is transmitted to relay valves which communicate compressed air from storage reservoirs to vehicle brakes. It will be appreciated, however, that the invention may relate to similar environments and applications.
A modulator relay valve for ABS brake systems typically includes an impermeable or solid walled piston or flexible diaphragm that selectively moves during normal service braking to establish communication among supply, delivery, and exhaust ports. The piston is responsive to a control signal provided, for example, from a foot brake valve or trailer control valve. The piston then selectively activates an inlet/exhaust valve to selectively connect the supply, delivery, and exhaust ports. In response to an antilock control event, a solenoid control assembly provides for a rapid pulsing of the brake application. That is, if an antilock event is sensed, an electronic control unit sends suitable signals to solenoid valve assemblies associated with the modulator. The valve assemblies provide an electro-pneumatic interface between the electronic control unit and the airbrake system. If an impending wheel lockup is sensed, the antilock controller immediately begins to modify brake application using the modulator. Air on one side of the modulator piston is controlled by selectively opening and closing the supply and exhaust solenoid valve assemblies. Coils associated with the respective solenoid valve assemblies are quickly energized or deenergized in a predetermined sequence by the controller. When the solenoid coil is energized, a core or shuttle is moved to either open or close an associated air passage. This either opens or closes the exhaust passage or reapplies air pressure to the brake actuator. By opening or closing the solenoid valves, the anti-lock controller simulates brake xe2x80x9cpumpingxe2x80x9d but at a rate substantially faster than the driver of a vehicle could actually pump the brakes to avoid skidding.
To achieve good ABS performance in air brake vehicles, a significant actor is the ability to rapidly exhaust service air from the brake chamber. In known two solenoid relay valve arrangements, control air from a relay valve control cavity is exhausted through an orificed exhaust solenoid passage. As will be appreciated, the orificed exhaust passage is relatively small. One proposed solution is to employ a larger solenoid, i.e., a solenoid having a larger orifice or exhaust passage, so that the passage would not serve as a bottleneck for the exhaust function during an antilock control event. However, a larger solenoid is less efficient and requires additional power to operate. It is for these reasons that present arrangements use an exhaust solenoid of a predetermined size and exhaust the control air from the relay valve control cavity through the exhaust solenoid passage. Thus, any improvement that addresses these concerns would be desirable, particularly if easily incorporated into an existing modulator valve without substantial modification.
The present invention contemplates an improved modulator relay valve employing a quick release valve in the control air circuit to allow control air contained therein to escape directly to atmosphere.
In accordance with a preferred embodiment of the invention, a quick release valve is interposed between the control cavity and the exhaust solenoid. In this manner, a majority of the control air contained in the cavity is permitted to escape directly to atmosphere through the quick release valve. The exhaust solenoid passage need only exhaust the relatively small volume of air disposed between the quick release diaphragm and the supply solenoid seat.
According to another aspect of the invention, the conventional antilock braking system is easily modified to incorporate this improvement.
A principal advantage of the invention is the ability to improve ABS performance on air braked vehicles.
Another advantage of the invention resides in the ability to achieve improved exhaust of control air from the relay valve control cavity without increasing the size and power constraints associated with the present solenoid valve assembly.
Still another advantage of the invention is the ability to easily modify the existing system to incorporate this feature.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description. dr
The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification. The preferred embodiment is illustrated in the accompanying drawings and forms a part of the invention, wherein:
FIG. 1 is a schematic representation of a prior art, two solenoid modulating relay valve assembly shown in a normal service application position;
FIG. 2 is a view similar to FIG. 1 illustrating the relay valve in a balanced or hold position;
FIG. 3 illustrates the prior arrangement in a service application release position;
FIG. 4 illustrates ABS operation where the exhaust port of the solenoid assembly is opened to simulate pumping of the brakes;
FIG. 5 is a schematic representation of the new invention; and
FIG. 6 is a graphical representation of the improved exhaust feature provided by the present invention.